1. Field of the Invention
The present invention relates to a lock structure for fixing and locking a member to be fixed such as a bearing screwed on a rotary shaft, by thrusting the fixed member in the axial direction.
2. Related Art
When a nut screwed on a bolt or a screw shaft is fastened, a stress in the thrusting direction is generated in the nut so that a frictional force is generated between the screwed face or the nut and the fixed member to stop the turn of the nut. In short, the fixed state by the nut is held. It is, however, known that if a vibration or impact is applied to that nut or screw shaft, the thrusting force is instantly dropped by an elastic deformation so that the nut is accordingly turned to get loose. In order to prevent this looseness of the nut, there has been known in the prior art the double lock nut in which a lock nut different from the fastening nut is used so that the fastening nut and the lock nut are screwed in their thrusting directions thereby to establish a high frictional force on their individual screwed faces.
According to a lock nut structure of the prior art, for example, a fastening nut 101 is fastened so far on a bolt 100 as to come into abutment against a washer 102, as shown in FIG. 7, and a lock nut 103 is then fastened so far as to come into contact with the fastening nut 101. Next, with the fastening nut 101 being slightly returned or being fixed by a wrench, the lock nut 103 is further fastened by the wrench. Thus, stresses in the upper direction (or X-direction) and in the downward direction (or Y-direction) of FIG. 7 are generated in the fastening nut 101 and the lock nut 103 thereby to thrust them into contact. As a result, the screwed face 104 of the upper lock nut 103 is forcibly thrust upward (in the X-direction) of FIG. 7 by the screwed face 105 of the bolt 100, and the screwed face 106 of the fastening nut 101 is forcibly thrust downward (in the Y-direction) of FIG. 7 by the screwed face 105 of the bolt 100. Thus, the facial pressure and the frictional force on the screwed faces rise to prevent the turns or looseness of the fastening nut 101 and the lock nut 103.
In Japanese Utility Model Laid-Open No. 6-18719, on the other hand, there is disclosed a nut locking structure in which the end face of a lock nut contacting with a fastening nut is an inclined face obliquely intersecting the axis of the lock nut.
According to this structure of Japanese Utility Model Laid-Open No. 6-18719, the fastening nut is fastened on a bolt, and the lock nut is fastened. From the instant when the lock nut abuts the fastening nut, the inclined face of the lock nut is turned by the clearance of the meshing portions of the lock nut and the bolt while being inclined in the direction to take facial contact with the end face of the fastening nut. As a result, a bending moment acts on the bolt, and a reaction to the bending moment acts on the bolt to fix the lock nut and the fastening nut.
However, what is mainly intended by the double lock nut structure of the prior art is the function to lock the fastening nut 101 such that the fastening nut 101 is thrust downward (in the Y-direction of FIG. 7) by the lock nut 103. However, the fastening nut 101 thrusts the fixed member or the like downward (in the Y-direction) of FIG. 7 and receives the reaction upward (in the X-direction). If the fastening nut 101 is thrust downward (in the Y-direction) by the lock nut 103, therefore, the reaction from the fixed member is received by the lock nut 103. As a result, the fastening nut 101 is just interposed between the lock nut 103 and the fixed member so that it does not perform the locking action. Thus, there is no locking function between the fastening nut 101 and the lock nut 103 so that the fastening nut 101 or the lock nut 103 is easily loosened when a vibration is applied thereto.
On the other hand, let the case be considered, in which the fastening nut 101 is fastened and then locked by the lock nut 103, as shown in FIG. 7. Then, the screwed face 106, as held in contact by the fastening nut 101, is released by the lock nut 103 to lower the double nut effect. Moreover, the fastening nut 101 is fastened with its end face being unstably inclined.
In the structure of Japanese Utility Model Laid-Open No. 6-18719, on the other hand, the abutting faces of the two nuts are inclined in the radial direction. As the lock nut is fastened, therefore, there increases the bending load on the shaft on which those nuts are screwed. This raises a disadvantage that the deflection of the shaft increases.
In the prior art, moreover, there is known a structure in which set screws 111 of a precision lock nut 110 are inserted radially of the precision lock nut 110 to thrust a threaded shaft 112. In the construction of this kind, however, when the set screws 111 are fastened, the individual axial forces and the individual radial forces of the set screws 111 grow different, as indicated by arrows in FIG. 8, because the inclinations of the threaded faces thrust by the set screws 111 are different for the individual set screws 111. This established a deflection in the threaded shaft 112. When the set shoes 111 shown in FIG. 8 are fastened, more specifically, the directions and magnitudes of the loads along the threaded face are different for the individual set screws 111 so that the differences act as the bending load on the threaded shaft 112 thereby to deflect the threaded shaft 112. As a result, the shaft is so largely deflected that it cannot be employed as a rotary shaft rotating at a high speed.
Thus in the precision lock nut 110 of the prior art, if the set screws 111 are adjusted to stress the correction of the deflection of the threaded shaft 112, the set screws 111 cannot be sufficiently fastened for the locking purpose so that the nut gets loose. This makes it necessary to perform the fastening operation by the set screws 111 in cooperation with the locking action of the nut and the correction of the deflection of the shaft. As a result, there is a problem that it is obliged to perform the difficult fastening works taking a long time.